MOSCOW, June 20 (Reuters) - Russia"s ambassador to the United States, Anatoly Antonov, was in an optimistic mood ahead of his return to Washington on Sunday, expecting meetings scheduled with U.S. colleagues next week to be constructive, the RIA news agency reported. President Vladimir Putin and his U.S. counterpart Joe Biden agreed to return their respective ambassadors to Washington and Moscow during talks in Geneva on Wednesday, a first summit between the two that they both described as pragmatic rather than friendly. read more Moscow recalled Antonov for consultations after Biden said in March that he believed Putin was "a killer". The U.S. ambassador later returned to Washington for consultations too. "There is a lot of work to be done. We are counting on progress," RIA cited Antonov as saying before he boarded a flight to the United States. Antonov said he was returning with an optimistic mindset and that meetings would begin on Monday and continue throughout the week.